1. Field of the Invention
The present invention relates to a battery system including a battery pack, for use in a camera for electric power supply to various electric and electronic components provided in the camera body of a still camera, and more particularly to such battery system provided with means for measuring the remaining capacity of the battery.
2. Related Background Art
Also in the field of still cameras, there have recently been marked introductions of electronic systems, as in the equipment of other fields. For this reason, various electric and electronic components, such as focal plane shutter, automatic exposure control mechanism, automatic film winding mechanism etc., are incorporated in the camera body as the loads for battery power source. Such transition toward the electronic systems is imposing various requirements on the battery to be incorporated in the camera body, such as a larger capacity, a lower cost, and a structure of easier use and better appearance.
The battery conventionally used in such still cameras has usually been UM-3 type which relatively easily available, and such battery is either directly loaded in a battery chamber formed in a part of the camera body or loaded in a battery pack that can be loaded into the camera body. The camera utilizing such battery is usually equipped with a simple battery check circuit for detecting the level of exhaustion of battery, and said circuit can be activated by the shutter release button of the camera or by an exclusive checking button and shows the result of checking in the view finder or in an indicator provided on the outside of the camera. The battery checking for detecting the level of exhaustion of UM-3 battery needs only to measure the open terminal voltage of the battery, because of discharge characteristics thereof, and requires only a simple circuit in the camera body.
In such still cameras, however, instead of primary battery that can only be used one time, such as UM-3 battery, there is desired the use of a rechargeable secondary battery pack, such as of nickel-cadmium batteries, because of a lower running cost, superior low temperature characteristics and preference by professional photographers.